Low-Energy Consumption With Closed-Circuit Desalination

Abstract

Since the inception of reverse osmosis (RO) for desalination in the late 1950s, basic membrane desalination processes have remained essentially unchanged, despite improved membranes and energy recovery devices. Conventional RO is a hydrodynamic plug-flow process with pressurized feed to semipermeable membranes split into two outlet streams—one of pressurized brine and the other of unpressurized permeate. The energy that remains in the pressurized brine stream must be recovered with energy recovery devices or lost across a brine valve. A new desalination technique—a continuous closed-circuit desalination (CCD) process—operates on the basis of relatively low average feed pressures and other operating advantages of batch RO with the continuous flow rates of feed and permeate of conventional RO. This article provides an overview of the CCD process, presents experimental data from operating CCD processes, and establishes the principles on which the technology can be applied to satisfy a wide range of desalination requirements.